


A New Experiment

by LittleQuail



Category: Undertale (Video Game)
Genre: Cunnilingus, Double Penetration in One Hole, Orgasm Delay/Denial, Other, Tentacles, lmao this is stupidly long
Language: English
Status: Completed
Published: 2015-12-01
Updated: 2015-12-01
Packaged: 2018-05-04 07:22:24
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,117
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/5325518
Author URL: https://archiveofourown.org/users/LittleQuail/pseuds/LittleQuail
Summary: <blockquote class="userstuff">
              <p>Sequel to Study You</p><p>While you have been hard at work at school, Gaster has been hard at work making something new for you.</p>
            </blockquote>





	A New Experiment

**Author's Note:**

> uhh so ive been extremely restless lately and i needed something to do so i wrote this.. its really dumb im sorry im no good ;o; Thanks for reading!

It had been a few weeks since your encounter with the skeleton scientist and it had been on your mind ever since. Every day when you came home from your classes, you looked around for the monster, leaning back in your bed just to see if he would come back. Eventually you gave up one day, simply sitting at your desk to do your work instead of your sleeping space.

You were working on a paper due the next day that you had put off the entire week, as per usual. Typing away at your computer, you realized it was darker in your room than normal. You don’t think much of it, simply chalking it up to the sun going down earlier than usual because it was winter. You turned on a lamp, or at least, you tried to. It clicked, but nothing happened. 

“Huh. That’s weird. Maybe I unplugged it?” You didn’t really think so, but you checked under your desk anyway. Nope, it was still plugged in. You scratched your head and sat back up, letting out a sharp yelp as a large black shape appeared in front of you, nearly straddling your lap. It took you a moment but your heart started to race when you realized you knew this mass. 

“Gaster! You’re back!” You tried to keep your face neutral, but your voice showed your excitement. His form solidified and he gave you a wide smile as his face formed. 

[Y/N. IT’S GOOD TO SEE YOU AGAIN]. It took you a moment to get used to his static-filled voice once more, it was a little jarring at first. [I HAVE BEEN WATCHING YOU AND I’VE SEEN HOW MUCH YOU’VE WANTED ME. WAITING FOR ME TO COME BACK, EVEN.] He tilted his head. [CURIOUS. I DO WANT TO LEARN MORE ABOUT YOU, IF IT’S ALRIGHT WITH YOU. I’VE BEEN PREPARING A NEW EXPERIMENT.] 

You looked between the monster in your lap and your computer behind him. There was no way you were going to pass this up. “A new experiment? It won’t hurt, will it?” 

He pressed a black hand to your shoulder, leaning in. [NOT IF I CONDUCT IT RIGHT. IS THAT A YES?] 

You nodded. “Yeah. Yeah, yes, please Gaster, I’ve wanted this for weeks” Your cheeks were blushing with excitement as you laid one of your own hands on his chest. He closed the distance and pressed his bony smile to your lips, making you grin and push into him. His tongue slid out of his mouth, the sweet black licorice flavor bringing you back to the first time you tasted it. It slid over your teeth and against your own tongue. You realized this time that, unlike yours, his tongue was completely smooth, and glided easily around your mouth. 

He moved his hands down from your shoulder to your breasts, squeezing them gently. You let out a moan around his tongue, rubbing your own hands on his chest. He reached back up and pushed you down onto your...bed? Weren’t you just by your desk? You back up from him and the kiss and look at him quizzically. He laughed, which sounded like it was covered in rough static. 

[THOUGHT SANS WAS THE ONLY ONE WITH TELEPORTATION?] He kissed your cheek. [I HAVE SO MANY THINGS THAT YOU DON’T KNOW ABOUT YET.] He trailed his tongue down your neck and gave a nibble, sending a shiver down your spine. His hands grazed the bottom of your shirt, and at your nod he lifted it up and over your head, quickly grasping onto your boobs. He drifted his fingers around your straps and undid the clasps holding your mounds up. Once it was slipped off, he pinched your sensitive nipples and you gasped, gritting your teeth together. He brought out his tongue once more and wrapped it around your breast, massaging it with his long tongue. You had been wanting him for so long that you didn’t stifle any of your sounds, letting out a long sigh, punctuated at the end with a muffled something. He looked up at you. 

[WHAT WAS THAT? I DIDN’T QUITE CATCH IT.] You squirmed, feeling embarrassed under his gaze. “M-More, I want more of you!” You couldn’t believe you were so turned on already, you were just ready for him. He gave you a chuckle. 

[THEN I THINK YOU’LL LIKE THIS NEW EXPERIMENT.] He reached down and behind you, gripping your ass before lifting you up. Another hand appeared beside you and unbuttoned your pants, slipping them off. You looked at his other hand with amazement. “How did you do that?” 

He wiggled around his fingers in his extra hand, giving a small smile. [LIKE I SAID, I HAVE MANY THINGS YOU DON’T KNOW ABOUT.] You reached up and grabbed his extra hand, two more appearing next to him to continue working on your pants. His hand by your face explored your cheeks, traveling down to your lips. You opened you mouth and the fingers stuck themselves in, pressing on your tongue and traveling around your molars. You closed your mouth around the digits and sucked, making Gaster give out a moan, a darkness rushing to his cheeks. You continued with your motions, wrapping your tongue around one of his fingers. That got a nice sharp noise out of him. You tried not to laugh but a giggle came out anyway, causing him to laugh a little bit too. He leaned in and nuzzled his mouth against your forehead. 

[YOU ARE JUST AN INTERESTING LITTLE THING, AREN’T YOU?] He kissed your cheek, then your neck, down to your chest, past your belly button, and finally to your panties. You realized that during your time with his hand he had gotten everything all ready as far as clothing goes. He kissed your hipbone, then your thigh, going right around where you wanted him to be. Finally, he gave in to your needs and pressed a kiss to your heat. You squeezed your legs and lifted your hips slightly, giving him more access to your pussy. 

He took this opportunity and licked from bottom to top, making you groan out. He pulled down your now-soaked underwear and threw them off the side of the bed. He stuck his head back between your legs and gave a solid lick, giving a low groan as he tasted your juices. 

[OH HOW I’VE MISSED THIS TASTE. I’VE MISSED YOU, Y/N.] His voice went straight to your crotch, making you even more wet. He rubbed his thumb over your clit, his tongue making quick use of your slit. He went in and swirled his tongue inside of you, making you give little gasps, grasping his skull and nearly shoving his face into you. “I-I’ve missed, ah, I’ve missed you toO AAah, aah!” You could feel your orgasm coming close, so you wiggled your hips and tried to get more friction between the two of you. He seemed like he could tell as well, so he stopped. You let out a groan, crossing your arms. “Come on, I was so close!” 

He laughed, sitting up. [I THINK YOU’RE READY FOR THE EXPERIMENT NOW.] As he was sitting up, he revealed what he was hiding. Not just one tentacle dick, but two, and they were both much larger than the last one you had seen. “Are you sure that’s going to fit?” 

He nodded. [I’VE DONE CALCULATIONS BASED ON OUR LAST EXPERIENCE AND KNOW YOUR LIMITS NOW.] He braced himself against your legs, positioning himself. [ONLY IF YOU WANT THIS. I WANT YOU TO BE OKAY WITH IT.] You nodded, trying to relax yourself as much as you could. He moved forward and put one of the tentacles halfway into your slit, you letting out a soft sigh as it stretched you out. [ARE YOU READY FOR THE OTHER ONE?] “Yeah, I think so.” With that, the other tentacle slid into your pussy, making you let out a hiss as pain turned into pleasure. It took you a moment to stretch all the way out, but you nodded towards him once you were ready. 

He moved out a little bit before slamming into you to his full hilt, making you cry out. It felt like it was reaching all the way inside of you, He pulled out half way before pressing back into you again, slower this time, but still pushing himself way in there. Your tongue lolled out of your mouth, eyes rolling back. Gaster pounded into you, the bulge in your pussy writhing with the tentacles as they moved around inside of you. He had his hands firmly grasped on your thighs, but another one appeared, the others having dissipated earlier. This new one hovered over your clit, lightly pressing against it. You yelled out in pleasure, everything building up and you could feel yourself starting to snap. 

“Gaster I-I think, I think I’m gonna-!” He slowed down, grinning down at you. [YOU WILL COME WHEN I SAY SO, Y/N. AND IT’S GOING TO BE A LITTLE WHILE MORE.] He pulled one of his tentacles out and jerked it off himself, getting a mixture of your juices and his precum on his fingers. He displayed his hand to you. [LICK IT CLEAN, IF YOU WOULD.] 

You did as told, taking his fingers in your mouth and sucking on them, licking them clean. Even his weird tentacle juices tasted like licorice and you wanted to lick him forever. He started to pound into you again, the other tentacle making lewd slapping noises as it hit your stomach. You opened your mouth as you couldn’t stop making noises. His fingers caressed your cheek, one of his hands finding its way from your thigh to your hand. You entangled your fingers, giving it that much more meaning.

He slipped the other tentacle back in, more coming out of his back, much larger and stronger, enveloping you in their grasp. He pulled you up and he laid down so you were riding him, letting your wanton noises slip carelessly out of your lips. You ground your hips into him, moving them in a circle before going back up and grinding on him. He let out a sigh, seeming to sink lower and lower into the sheets on your bed. He pushed up his hips into yours and he hit that spot inside of you that sent you crazy. 

“Please, Gaster, please more, right there! Fuck me harder, oh please!” You couldn’t believe the lewd words coming out of your mouth but there they were, in the air, for him to hear and get more excited because of it. He thrusted up, grunting. It wasn’t long before you two were just a mess, moaning each other’s names, your hair getting in your face, sticky wetness coating both of you. You could feel yourself coming undone, and you told him so.

“I’m gonna, Gaster, I’m gonna co-ome!” With that he pumped up into you one last time and you yelled out his name, your back arching in the air as he hit your gspot. A few thrusts after you, he came as well, the sticky goop coming out of his tentacles starting to feel familiar to you. You both took a couple moments to catch your breath, him using his extra tentacles to lay you down and pull out of you. A slimy sound came from your nethers, with black goo coming out. It was a good thing he couldn’t get you pregnant. 

[I WILL BE RIGHT BACK. PLEASE, GET COMFORTABLE.] That wasn’t even a question. You snuggled into your bed, your aching legs and back welcoming the sweet comfort. You weren’t sure where he went, as he had simply disappeared, but when he came back, he had a warm and damp cloth and he cleaned you up, wiping away everything he left behind. He himself was clean and put away. 

He bent down and kissed your forehead. [I AM GLAD THIS EXPERIMENT WAS A SUCCESS. REST, Y/N, I’M SURE YOU NEED IT. I WILL SEE YOU AGAIN.] He pulled your blanket up and let you be once more.

In the morning, you remembered your paper you were supposed to be working on. You scrambled out of bed, seeing if you could maybe form some kind of lame excuse as to why it was late. But as you looked in your assignment list online it looked like it was turned in last night - all completed and better than anything you could have written. You gave a sigh of relief and crawled back into bed, looking forward to sleeping the rest of the morning.


End file.
